Storage reservoirs are used to pick up and reprocess blood shed in the operating field. The blood is processed by removing the foam, which is easily generated by sucking operations, and also by filtering the defoamed blood before re-introducing it into the circuit and ultimately into the patient.
The basic need for such reservoirs is to permit collection of shed blood and then to feed it back into the patient. In many cardiovascular operations, too much blood is shed to permit outright discard, as is done in most other surgical procedures. On the other hand, such shed blood is apt to contain cellular and other debris which would embolize if infused directly back into the patient. Moreover the process of sucking the blood up is hemolytic in itself -- to the point of causing more damage even than pumps or oxygenators. Much foam is ordinarily generated and the blood which is actually suspended in the foam has been subjected to high shear rates as the film bubbles are formed and also there is an undesirable contact with an air interface. These factors cause blood damage and, although foaming has in the past been controlled by adding silicone antifoam agents, there are some reports that silicone itself is responsible for blood damage, and it is undesirable to have such chemical antifoams enter the body in small amounts, particularly as droplets or micro emboli.
There is now provided a combination cardiotomy reservoir and blood filter. The device serves as a storage reservoir for blood picked up from the operating field and then processes the blood by separating the foam and removing cell debris by filtration before reintroducing the blood into the circuit. In this novel device the reservoir and filter are combined into an integral unit; and the foam is killed and collected externally, then discarded.
Thus, the present invention provides a device which allows storage and return of blood to the patient with as little additional damage as possible. In contrast to separate filters requiring several hundred milliliters of blood for priming, the new device requires no additional priming volume because the filter is in the body of the reservoir. Other advantages in the new device are in greater ease of usage, improved ease of maintaining sterility, and ready adaptability to circuits which contain membrane oxygenators, where a filter in the primary circuit is of doubtful value. In addition, since defoaming is not needed in the main flow circuit, as in the case of bubble oxygenators, the introduction of chemical foam killers into the patient can be avoided entirely.